It is not uncommon for businesses or departments within a business to send a group gift for special occasions. If you receive a gift from a group of people, it is proper etiquette to send a thank you note.
If the gift was sent from four or less people, an individual thank you note should be sent to each person.
If the gift was sent from five or more people, one thank you note, which may be posted on the office bulletin board, is appropriate.